Method of producing corrugated cases



Aug. 8, 1939. A. D. FORBES METHOD OF PRODUCING CORRUGATED CASES Filed Sept. 16. 1957 WITNESSES: INVENTOR Aggfl/ res. 2 ATTORNEY Patented Aug. 8, 1939 METHOD OF PRODUCING CORRUGATED CASES Allan D. Forbes, Sharon, Pa., assignor to 'Westinghouse Electric, & Manufacturing Company, East Pittsburgh, Pa., a, corporation of Pennsylvania Application September 16, 1937, Serial No. 164.153

1 Claim. (o1. 113-120) This invention relates to the method of producing corrugated cases for electrical apparatus. According to the present practice of making corrugated cases for dissipating heat developed in enclosed electrical apparatus, the corrugations may be bodily pressed into a metal blank by suitable dies. fects a considerable flow of metal in the blank and is difllcult to control because of the resistance of the metal to deformation.

Usually wherethe corrugations or flutes, as they are sometimes termed, are pressed directly from the blank, the opposite edges of the blank are initially so notched in spaced relation that the notches are disposed between the flutes or corrugations. These notches are so shaped that when the flutes are pressed into the blank the accompanying flow of metal causes the curved edges of the notches to form straight meeting edges.

The notches stamped or punched in the sheet in order to effect this operation are widest at the edge of the blank and taper to exceedingly sharp points at their apex. Because of this sharp point at the apex of the notch, splitting or, fracture of the sheet metal blank at the notches is often found. This is because the high pressures necessary to press the corrugations or flutes and the accompanying flow of metal tend to split the blank at the sharp points of the notches.

An objectof this invention is the provision of a method for producing corrugated cases for electrical apparatus.

Another object of this invention is to provide a method for producing a corrugated case for electrical apparatus from a sheet metal blank without a substantial flow of metal.

One objects of this invention will become apparent from the following description when taken in conjunction with the accompanying drawing,

in which:

Figure 1 is a plan view of a section of sheet' metal blank which has been partially formed in accordance with the teachings of this invention; Fig. 2 is an end elevational view of the sheet .15 vmetal blank illustrated in Fig. 1;

' Fig. 3 is a view in section of a corrugation taken along the line I[I--III of Fig. 1;

Fig. 4 is a view in section of a corrugation along the line IV-IV of Fig. 1; 50 Fig. 5 is a view in elevation of the casing; and Fig. 6 is a plan view of the casing illustrated in Fi 5. I

Like reference characters refer to similar parts of the difierent figures of the drawing.

55 Referring to the drawing, and particularly to- The pressing of the corrugations ef- Fig. 5 thereof, this invention is illustrated with reference to the method of producing the case ll) of a distribution transformer. In the particular embodiment illustrated, the case comprises a case wall II, a top or cover and a base [6 disposed 5 thereon and preferably secured thereto as by welding.

As illustrated, a series of corrugations or flutes l8 which function to increase the radiating surface of the case for dissipating heat from the en- 10 closed apparatus, are disposed in spaced relation about the case and between the cover and base of the case. In the particular case illustrated in Figs. 5 and 6, the corrugations or flutes l 8 are not disposed completely about the case but instead, 15 a space l9 is'provided having asmooth surface to which suitable hanger brackets 20 may be secured as by welding.

Referring to Fig. 1 of the drawing, the wall of the case may be produced from a sheet blank 20 22 of any suitable metal. Notches 24 of a suitable shape are disposed in spaced relation to each other in the opposite edges comprising the upper and lower edges of the blank- The notches 24 may be punched, out or otherwise formed in the 25 opposite edges of the blank as shown in the lefthand portion of Fig. 1 of the drawing. In forming the notches it is desired that the notches be substantially U-shaped with an inner or base portion 26 simulating the shape of a Gothic arch, 30

the purpose of which will be explained more fully hereinafter. The depth of the notches to the curved inner or base portion will depend upon the distance desired between the ends of the finished flutes and the edges of the blank.

After the notches 24 are formed in the sheet 35 metal blank, the notched blank may be subjected to the action of suitable dies to press corrugations 28 in spaced relation to each other in the blank. The size of the corrugations desired-will determine the size and curvature of the notches 24 in the blank. The relationship between the corrugations and the size of the notches may be easily determined experimentally. As illustrated in the central portion of Fig. 1, each of the corrugations 28 extends from the upper edge of the blank to the lower edge of the blank in spaced relation corresponding to the spaced notches 24 and includes a notch formed in each of the opposite or upper and lower edges of the blank.

As the corrugations 28 are formed in the blank the edges of the notches 24 are raised above the original plane of the blank and because of the shape of the notch are brought closer together as illustrated in the central portion of Figs. 1 and 2.

Because of the Gothic arch shape of the notch; the metal will not split or fracture at the apex of the notch when the sheet metal is corrugated. as described, since the apex is not an exceedingly" sharp point and a flow of metal is not there encountered.

After the corrugations are formed as described, the ends of the corrugations beginning at the apex of the notch 2| may be subjected to a suitable forming operation as by a die to further draw the edges of the notch together forming tapered ends on the corrugations and returning the end portions of the corrugations to the original plane of the sheet metal blank, as illustrated in the right-hand portion of Fig. 1 and in Fig. 4. The open ends of the notches are thus drawn together in the original plane of the sheet metal blank. As will be evident, because of the shape of the notch the drawing of the edges of the notch together as described will be accomplished without a substantial flow of the metal of the blank.

with the ends of the corrugations thus tapered and the edges of the notches drawn together, the seams formed may be welded to seal the ends of the corrugations or flutes and form a solid smooth edge on the blank. The blank containing the sealed corrugations or flutes may then be bent to form the desired shape of the case wall, the meeting edges being suitably sealed as by welding. As will be understood, the case wall may be formed from a single corrugated blank or from a plurality of blanks, and may or may not have a smooth surface for the attachment of the hanger brackets as desired. After the case wall is formed the cover and base may be disposed on the wall and sealed thereto as by welding.

The method of this invention provides for easily, efliciently and economically producing corrugated cases without necessitating a substantial flow of metal in the blank employed. Flaws and fractures are not encountered in making the corrugations because of the particular shape of the notch employed, thus eifecting a considerable saving in material.

Although this invention has been described with reference to a particular method, it is or course not to be limited thereto except insofar as is necessitated by the prior art and the scope of the appended claim.

I claim as my invention:

In the method of producing a corrugated case for electrical apparatus. the steps comprising,

forming notches in spaced relation to each other in opposite edges of a sheet metal blank, each of the notches being substantially U-shaped with an inner' edge or base simulating the shape of a Gothic arch having its edges in the plane of the blank, forming corrugations in spaced relation in the sheet metal blank so disposed as to extend between the opposite edges of the blank and to wholly include a pair of the notches formed in the opposite edges of the blank within each corrugation, drawing the edges of the Gothic arch base of each of the notches in each of the corrugations together without a substantial flow of metal to close the ends the corrugations to form tapered ends and return the outer edges of the notches to the original plane of the sheet metal blank whereby the corrugations terminate within the blank at a distance spaced from the edges thereof, and welding the edges of each of the drawn notches throughout its length to seal the corrugations and provide a solid edged blank ALLAN D. FORBES. 

